Soil Conservation

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Soil Conservation
Safeguarding soil from depletion or
deterioration
Sustainable Soil Use
A nation that destroys its soil destroys
itself Franklin D. Roosevelt, 1937
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Soil Quality
The capacity of a soil to sustain biological
productivity and diversity, maintain
environmental quality, and promote plant and
animal health
Anything that affects soil quality can affect
sustainable use of soil
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Limitations to sustainable soil use
(Limitations first, then some solutions)
1. Soil Erosion 2. Salinization 3. Nutrient
Removal 4. Urban Encroachment 5. Contamination /
Pollution
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Wind Erosion in New Zealand
Water erosion
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Raindrop impact loosens soil particles-- particles
can then either move down hill and knock other
particles loose, or enter soil pores, plugging
surface soil and encouraging more erosion
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Erosion is also associated with roads, landings,
wildfires other areas with bare soil
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Since 1945 ? 11 of earths vegetated surface
(? area of China India) has been degraded so
badly it will be very expensive or impossible to
fix.
In many areas, subsistence agriculture is
practiced.
But once the land is eroded, the soil is ruined
for farming and may be abandoned
Nevertheless, populations are still
increasing. especially in areas where
subsistence farming is important
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It is estimated that 1/5 of the worlds topsoil
has been lost since 1950!!

• Bangledesh
• population increasing and urbanizing
• soil degradation from ?farming intensity
• ?SOM, ?fertility estimated cost of soil
• degradation is 7.7 of GDP (2007)

• US
• Dust bowl of the 1930s

• China
• 1/6 land area gt serious erosion
• Atmospheric scientists in Hawaii can tell
  within a few days
• when the spring plough starts in N. China.

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Desertification The spreading of desert
conditions due to land degradation
Hillel 1991
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Earth's deserts and areas susceptible to
desertification
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Average soil formation rate
Geologic or natural erosion rate
.25 mm per year 2.5 Mg ha-1
or 1 ton per acre (includes rocky material)
USDA tolerable soil loss per year
11 Mg ha-1 !!
or 5 tons per acre !!
0.03 mm per year or 0.3 Mg ha-1
or gt0.1 ton per acre !! (not rocky material)
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In Texas, up to 60 tons of topsoil can be lost
to produce 1 ton of cotton
Average annual soil erosion in the US. Erosion
has declined but still exceeds the tolerable
limit of 5 tons per acre per year.
USDA, 1995
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Predicting Soil Erosion
Universal Soil Loss Equation (USLE) or
Revised Universal Soil Loss Equation (RUSLE)
A RKLSCP
A metric tons of soil lost per hectare per
year R rainfall erosivity K erodibility of
soil L length of slope S steepness of slope C
cover type P erosion control practices
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Limitations to sustainable soil use
1. Soil Erosion 2. Salinization 3. Nutrient
Removal 4. Urban Encroachment 5. Contamination /
Pollution
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2. Salinization
Did you know ...
Salt-affected soils are the 2nd largest cause of
soil degradation (after erosion)
?
Globally it removes about 3 hectares of land from
production every minute.
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The rising water table in a poorly-drained soil
infuses the root zone with salts.
Irrigation with water containing salts and
over-fertilization lead to salinization
Hillel 1991
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Lake Eyre, Central Australia
Murray River Basin, SE Australia
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Limitations to sustainable soil use
1. Soil Erosion 2. Salinization 3. Nutrient
Removal 4. Urban Encroachment 5. Contamination /
Pollution
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3. Nutrient Removal
If you harvest a crop you are removing nutrients
from that ecosystem For sustainable production
they need to be replaced
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Amounts of some nutrients removed by harvesting
over a 50 year period compared with weathering
release of nutrients in temperate areas (kg/ha)
P K Ca Mg
Deciduous Forest Harvest 10-20 60-150 175-250 25-100
Corn-wheat-soybeans 1200 2000 550 500
Weathering Rates 5-25 250-1000 150-1500 50-500
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4. Urban Encroachment
For example, LAS VEGAS
Las Vegas, 1972 pop. 273,000
Las Vegas, 1992 pop. 863,000
Las Vegas, 2000 pop. 1,560,000
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5. Contamination
FROM

• metals
• toxic organics
• over fertilization - nitrate, phosphate
• solid wastes

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toxicity symptoms in alder planted in mine
tailings
overfertilizing a lawn
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Current population gain is 78 million people per
year, or 214 000 /day 8 904 /hour. It is
predicted that world population will level off at
about 10 Billion. In next 30 years humans will
need as much food and fiber as they used in last
10 000 yrs.
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Soil degradation Poverty
Soil degradation is among the fundamental causes
of global unrest Rattan Lal, 2007,
President of SSSA
Our challenge is to produce and distribute enough
food, energy and necessities for all, without
ruining the resources used to produce them.
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So what do we do?
Prevent damage !!
Do the right thing at the right place
Use the best management practices

• Keep vegetation on site,
• Use cover crops,
• Conservation tillage, contour plowing.
• Don't excessively fertilize,
• Avoid compacting soil,
• Use compost..
• Build roads sparingly and carefully

e erosion w water s shallow, rocky c climate
Land capability classes
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What if damage is already there?
Reclaim or restore soils
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Repairing Soil
For eroded soil

• stabilize land - prevent further erosion
• establish vegetative or other cover
• repair topsoil - add organic matter

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For wind erosion, prevent further loss.
Use windbreaks, or keep soil covered.
Effect of a windbreak on wind velocity when
planted perpendicular to prevaling winds.
Chiras et al. 2002
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For water erosion, keep soil infiltration high,
control overland flow using vegetation, ditches,
contour plowing etc.
Decommisioning and restorating a logging road
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After mining

• stabilize waste
• stabilize or remove toxic metals
• restablish vegetation
• even better begin restoration with mining,
  recontour, clean wastes, replace topsoil,
  plant native vegetation

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With other types of contamination

• not always possible to repair- remove soil
• bioremediation - microbial degradation (oil)
• phytoremediation - using plants for reclamation

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If soil develops salinity

• install drainage
• leach slowly with clean water
• may need to add Ca to displace Na

If nutrient are being depleted

• replace nutrients with
• compost
• organic wastes
• fertilizers

Urban encroachment

• use zoning to protect
• floodplains, best soils, sensitive soils
  reclaim soils